Magnetic resonance system, and device and method for control thereof

Abstract

In a method for controlling a magnetic resonance system with multiple radio-frequency transmission channels, via which parallel RF pulse trains are emitted in operation, as well as a magnetic resonance system and a pulse optimization device therefor, RF pulse trains respectively include at least one radio-frequency pulse. The RF pulse trains are initially determined so that a minimum B 1 field maximum value is not exceeded by the radio-frequency pulse. In an examination subject-specific adjustment step, a current component-dependent B 1 field maximum value is then determined, and the radio-frequency pulse is temporally shortened, with its amplitude being increased dependent on the current component-dependent B 1 field maximum value.

I claim as my invention: 
     
       1. A method for operating a magnetic resonance system having a scanner comprising multiple radio-frequency (RF) transmission channels, said method comprising:
 via the multiple radio-frequency transmission channels, emitting respective RF pulse trains in parallel, each RF pulse train comprising at least one RF pulse that produces a B1 field; 
 in a processor, initially determining said RF pulse trains so that the at least one RF pulse in each of the respective RF pulse trains does not exceed a minimum B1 field maximum value; 
 with an examination subject located in the magnetic resonance scanner, operating the magnetic resonance scanner to determine a hardware component-dependent B1 field maximum value that is dependent on hardware components of the scanner; 
 in said processor, temporally shortening the respective at least one RF pulse in each of the RF pulse trains by increasing an amplitude of said at least one RF pulse dependent on said hardware component-dependent B1 field maximum value; and 
 from said processor, emitting control signals to operate the scanner to acquire diagnostic magnetic resonance data from the examination subject by emitting the respective RF pulse trains in parallel, each with the increased amplitude of the at least one RF pulse therein. 
 
     
     
       2. A method as claimed in  claim 1 , comprising:
 in said processor, initially predetermining a common reference pulse train for said multiple RF transmission channels, said common reference pulse train comprising at least one RF pulse; 
 in said processor, executing an optimization algorithm to determine a respective transmission scaling factor for each of said RF transmission channels dependent on a predetermined target magnetization in said subject, and calculating the respective RF pulse trains for the respective transmission channels dependent on said target magnetization and said reference pulse train; 
 in said processor, predetermining said reference pulse train to cause said minimum B1 field maximum value not to be exceeded by the respective at least one RF pulse of the respective RF pulse trains; 
 determining said hardware component-dependent B1 field maximum value based on the RF pulse trains for the respective transmission channels; 
 shortening the at least one RF pulse in the reference pulse train to cause an amplitude thereof to be increased dependent on said hardware component-dependent B1 field maximum values, thereby obtaining a modified reference pulse train; and 
 in said processor, calculating the respective RF pulse trains for the respective transmission channels using the modified reference pulse train and the transmission scaling factors. 
 
     
     
       3. A method as claimed in  claim 2  comprising maintaining said reference pulse train unchanged when shortening said at least one RF pulse in the respective RF pulse trains. 
     
     
       4. A method as claimed in  claim 2  comprising emitting said at least one RF pulse in said reference pulse train as a slice-selective RF pulse, and emitting a slice selection gradient pulse in parallel with said slice-selective RF pulse, and adapting an amplitude of said slice selection gradient pulse to an amplitude of said slice-selective RF pulse while maintaining a time duration of said slice selection gradient pulse constant. 
     
     
       5. A method as claimed in  claim 4  comprising emitting said slice-selective RF pulse centrally, with respect to time, relative to the slice selection gradient pulse emitted in parallel therewith. 
     
     
       6. A method as claimed in  claim 4  comprising emitting said slice-selective RF pulse as an excitation pulse, and emitting at least one dephasing pulse and adapting said at least one dephasing pulse dependent on a change in the amplitude of the slice selection gradient pulse emitted in parallel therewith. 
     
     
       7. A method as claimed in  claim 4  comprising increasing the amplitude of the slice-selective RF pulse dependent on a relationship between said hardware component-dependent B1 field maximum value and said minimum B1 field maximum value. 
     
     
       8. A method as claimed in  claim 1  comprising emitting said at least one RF pulse in each of said pulse trains as a slice-selective RF pulse, and emitting a slice selection gradient pulse in parallel with said slice-selective RF pulse, and adapting an amplitude of said slice selection gradient pulse to an amplitude of said slice-selective RF pulse while maintaining a time duration of said slice selection gradient pulse constant. 
     
     
       9. A method as claimed in  claim 8  comprising emitting said slice-selective RF pulse centrally, with respect to time, relative to the slice selection gradient pulse emitted in parallel therewith. 
     
     
       10. A method as claimed in  claim 8  comprising emitting said slice-selective RF pulse as an excitation pulse, and emitting at least one dephasing pulse and adapting said at least one dephasing pulse dependent on a change in the amplitude of the slice selection gradient pulse emitted in parallel therewith. 
     
     
       11. A method as claimed in  claim 8  comprising increasing the amplitude of the slice-selective RF pulse dependent on a relationship between said hardware component-dependent B1 field maximum value and said minimum B1 field maximum value. 
     
     
       12. A method as claimed in  claim 1  comprising emitting each RF pulse train as a part of a pulse sequence comprising an echo time, and maintaining said echo time unchanged when shortening said at least one RF pulse in each of said RF pulse trains. 
     
     
       13. A method as claimed in  claim 1  comprising, in said processor, calculating said B1 field maximum value using at least one component protection model function that represents a maximum allowable voltage for a transmission component of said magnetic resonance system. 
     
     
       14. A method as claimed in  claim 1  comprising, in said processor, calculating said B1 field maximum value using spatially dependent sensitivity distributions of said multiple RF transmission channels. 
     
     
       15. A method as claimed in  claim 1  comprising, in said processor, calculating said B1 field maximum value only for a locally limited region in said magnetic resonance system. 
     
     
       16. A pulse optimization device for operating a magnetic resonance system having a scanner comprising multiple radio-frequency (RF) transmission channels, said method comprising:
 an input interface configured to receive, for each of the multiple radio-frequency transmission channels, a respective RF pulse train, each RF pulse train comprising at least one RF pulse that produces a B1 field in said magnetic resonance scanner, wherein the at least one RF pulse in each of the respective RF pulse trains does not exceed a minimum B1 field maximum value; 
 a maximum value determination unit provided with data obtained by operating the magnetic resonance scanner with an examination subject located in the scanner, and configured to determine a hardware component-dependent B1 field maximum value that is dependent on hardware components of the scanner; 
 a pulse adaptation unit configured to temporally shorten the respective at least one RF pulse in each of the RF pulse trains by increasing an amplitude of said at least one RF pulse dependent on said hardware component-dependent B1 field maximum value: and 
 from said processor, emitting control signals to operate the scanner to acquire diagnostic magnetic resonance data from the examination subject by emitting the respective RF pulse trains in parallel, each with the increased amplitude of the at least one RF pulse therein. 
 
     
     
       17. A pulse optimization device as claimed in  claim 16 , comprising:
 said input interface being configured to receive a common reference pulse train for said multiple RF transmission channels, said common reference pulse train comprising at least one RF pulse; 
 a processor configured to execute an optimization algorithm to determine a respective transmission scaling factor for each of said RF transmission channels dependent on a predetermined target magnetization in said subject, and calculating the respective RF pulse trains for the respective transmission channels dependent on said target magnetization and said reference pulse train; 
 said processor being configured to predetermine said reference pulse train to cause said minimum B1 field maximum value not to be exceeded by the respective at least one RF pulse of the respective RF pulse trains; 
 said processor being configured to determine said hardware component-dependent B1 field maximum value based on the RF pulse trains for the respective transmission channels; 
 said processor being configured to shorten the at least one RF pulse in the reference pulse train to cause an amplitude thereof to be increased dependent on said hardware component-dependent B1 field maximum values, thereby obtaining a modified reference pulse train; and 
 said processor being configured to calculate the respective RF pulse trains for the respective transmission channels using the modified reference pulse train and the transmission scaling factors. 
 
     
     
       18. A magnetic resonance system comprising:
 a magnetic resonance data acquisition scanner comprising multiple radio-frequency (RF) transmission channels; 
 a control unit configured to operate said data acquisition scanner to emit, via the multiple radio-frequency transmission channels, respective RF pulse trains in parallel, each RF pulse train comprising at least one RF pulse that produces a B1 field; 
 a processor configured to initially determine said RF pulse trains so that the at least one RF pulse in each of the respective RF pulse trains does not exceed a minimum B1 field maximum value; 
 said control unit being configured to operate said data acquisition scanner with an examination subject located therein to obtain a hardware component-dependent B1 field maximum value that is dependent on hardware components of the scanner; 
 said processor being configured to temporally shorten the respective at least one RF pulse in each of the RF pulse trains by increasing an amplitude of said at least one RF pulse dependent on said hardware component-dependent B1 field maximum value; and 
 from said processor, emitting control signals to operate the scanner to acquire diagnostic magnetic resonance data from the examination subject by emitting the respective RF pulse trains in parallel, each with the increased amplitude of the at least one RF pulse therein. 
 
     
     
       19. A non-transitory, computer-readable data storage medium encoded with programming instructions, said storage medium being loaded into a computerized control unit of a magnetic resonance system, said magnetic resonance system comprising a scanner having multiple radio-frequency (RF) transmission channels, and said programming instructions causing said control unit to:
 operate the scanner to emit, via the multiple radio-frequency transmission channels, respective RF pulse trains in parallel, each RF pulse train comprising at least one RF pulse that produces a B1 field; 
 initially determine said RF pulse trains so that the at least one RF pulse in each of the respective RF pulse trains does not exceed a minimum B1 field maximum value; 
 with an examination subject located in the scanner operate the scanner to determine a hardware component-dependent B1 field maximum value that is dependent on hardware components of the scanner; 
 temporally shorten a respective at least one RF pulse in each of the RF pulse trains by increasing an amplitude of said at least one RF pulse dependent on said hardware component-dependent B1 field maximum value; and 
 from said processor, emitting control signals to operate the scanner to acquire diagnostic magnetic resonance data from the examination subject by emitting the respective RF pulse trains in parallel, each with the increased amplitude of the at least one RF pulse therein. 
 
     
     
       20. A method as claimed in  claim 1  wherein said at least one RF pulse in the reference pulse train has a flip angle prior to shortening said at least one RF pulse in the reference pulse train, and comprising shortening said at least one RF pulse in the reference pulse train to cause said RF pulse in the reference pulse train with the amplitude thereof increased to have the same flip angle as said at least one RF pulse in the reference pulse train prior to shortening thereof.